1. Field of the Invention
The improvement of the present application relates to the servicing of interrupt requests to a processor unit, and more particularly to the servicing of interrupt requests from apparatus which is alien to the operating system under which the processor unit runs, i.e. the operating system has no routines provided for servicing a request from the apparatus.
2. Prior Art
Most current data processing programs execute in one of two (or more) states, a supervisor state or a user state. Application programs run in user state, and functions such as the servicing of interrupt requests are performed by operating system routines running in supervisor state.
An application program contains instructions to attach to an I/O port, then opens the port, issues an I/O request in the form of a read, write or control. At that time the processor will take a task switch. When the operating system receives an interrupt signifying an I/O completion, then the operating system will put this information into a ready queue and sort by priority for system resources.
The operating system reserves all interrupt vectors for its own use; none are available for new features such as an external interrupt signifying an I/O request from another machine, such as a processor alien to the operating system.
Often a majority of the available interrupt vectors are actually unused, and these are set up to cause vectoring to a common error handler for `uninitialized` or `spurious` interrupts, as is the common practice in operating systems.
It is therefore the primary object of the present improvement to provide an improved method and means for servicing interrupt requests to a processor from apparatus alien to the operating system under which the processor operates.